1. Field
The following description relates to a method for protection switching in an Ethernet ring network, and more particularly, to a technique of selectively flushing a Filtering DataBase (FDB) by setting a Do Not Flush (DNF) bit of a protection switching message as necessary when a failed link is found.
2. Description of the Related Art
Since the G.8032 Ethernet protection system allows no loop of Ethernet rings, the G.8032 Ethernet protection system defines a logically blocked link called a Ring Protection Link (RPL) to logically block RPL ports. In a multi-ring where many rings connect to each other, each ring forms a bus phase and the entire network forms a tree phase. An RPL owner node periodically transmits a control message to a ring to which the RPL owner node belongs to inform that the network is in a stable state, and each node creates a Filtering DataBase (FDB) which is a forwarding table suitable for a phase configured with the blocked RPL ports.
If failure occurs in a specific ring, the blocked RPL ports are unblocked, and FDB information suitable for the changed network phase is reconfigured. In other words, nodes adjacent to a ring where failure has occurred block the corresponding ports and transmit Signal Failure (SF) messages to the neighboring nodes. The neighboring nodes that have received the SF messages flush their own FDB information, a RPL owner node unblocks the blocked RPL ports and thereafter, the nodes collect forwarding information suitable for a new phase using a MAC Source Address Learning Mechanism defined in an Ethernet bridge standard to thereby create FDBs.
However, since the nodes that have received the SF messages flush their own FDBs, the existing forwarding tables become disabled and accordingly all the nodes need new forwarding tables. Accordingly, the nodes should again start MAC source address learning. However, such frequent MAC source address learning causes a traffic overshoot in the network.